When one uncontrollably falls asleep every time they lay down flat, parallel to the floor, even if it is not a planned "nap time."
Roger: "Hey man, why weren't you in class today?"

Matt: "Dude, i laid down on the couch to watch TV and my horizontal narcolepsy kicked in... woke up 4 hours later."
by midleman08 May 12, 2010
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Once, I was listening to a friend's horizontal bop... it made me laugh so hard I crapped my pants.
by I like chocolate milk. August 15, 2005
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They only ever thought about who was doing the horizontal bop with who.
by The Return of Light Joker August 6, 2009
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John: Damn! Did you see that girl?
L: Yeah that thang swangin, I will go see if she is interested some horizontal refreshment.
by Hell owe December 13, 2014
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A shit that is horizontal.

A horizontal shit is essentially a turd that turned sideways while still inside the rectum, forcing it to come out horizontally, often rupturing the anus in the process. It often occurs when one has to keep themselves from defecating for extended periods of time.
"damn man, yesterday I had a horizontal shit so bad it made my ass look like the Japanese flag"
by LongWangChang February 22, 2016
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